1. Field of the Invention
The present invention relates to a split type ribbon optical fiber core cable in which a plurality of optical fiber tape core cables, each of which consists of a plurality of colored optical fiber core cables arranged in flat arrangement and united with each other, are arranged in a row, united with each other and capable of splitting apart from each other.
2. Description of the Related Art
Unexamined Japanese Patent Publication (kokai) No. Hei. 4-163411 discloses a conventional method for producing a split type ribbon optical fiber core cable which uses a split unit coated with a soft resin at a split position to avoid unnecessary splitting of the split type ribbon optical fiber core cable and to be capable of easily finding the split position as seen from its exterior. Also, in the method, the split unit and the optical fibers are completely coated with a hard resin so that the split position can be felt by and incorrect splitting avoided.
However, the above conventional cable tape has a drawback; splitting the cable tape may expose an optical fiber or detach an optical fiber from the coating resin.
These troubles arise because of the poor adhesion in the split position between the optical fiber surface and the united coating resin. Specifically, when the above split type ribbon optical fiber core cable is split, the coating resin peels off the optical fiber leaving a surface whose adhesion to the resin is relatively low, resulting in optical fiber detachment.
Also, Unexamined Japanese Patent Publication No. Hei. 4-166808 discloses another method in which the thickness of an ribbon optical fiber core cable is reduced to a value almost equal to the outer diameter of the optical fibers and the adhesion strength between the optical fiber surface and the coating resin is regulated to a value in a specific range in terms of 90.degree. peel strength so that the ribbon optical fiber core cable can be easily split when twisted.
However, in the above ribbon optical fiber core cable, there is the possibility that the cable tape may develop cracks when twisted.
The cracking occurs because the twisting of the ribbon optical fiber core cable imposes a strain on the coating interface within the ribbon optical fiber core cable.
Unexamined Japanese Patent Publication No. Hei. 1-138518 discloses a technique in which a bonding resin material having a different elongation coefficient is used to bond ribbon optical fiber core cables to each other in order to facilitate the splitting of the united ribbon optical fiber core cables.
However, in the above technique, use of a bonding resin having a reduced elongation coefficient results in cracking upon application of an external force.
This is because the bonding resin having a reduced elongation coefficient is more apt to develop cracks upon bending.